1. Field of Invention
The present invention relates to a fan and a motor control device, and in particular to a fan and a motor control device which drives a motor to operate via a voltage signal provided by a power factor correction circuit or via a pulse-width modulation signal and the voltage signal provided by the power factor correction circuit.
2. Related Art
Since the environmental protection regulations of every country have been rigid day by day, the trend of developing the driver of brushless DC motor is towards energy saving and superior quality of power source. Therefore, a power factor correction (PFC) circuit is normally disposed in the motor system for enhancing the quality of power source, reducing the harmonics of the motor system and reducing meaningless consumption (reactive power) of power source, so as to enhance the efficacy of the motor.
Please refer to FIG. 1, which shows a conventional brushless DC motor 54 which has the function of power factor correction. An alternating current power source 51 is commutated by a commutating circuit 52 (such as a bridge circuit) and then converted to be a direct current voltage VDC by a PFC circuit 53, so that the direct current voltage VDC works as a driving voltage for the brushless DC motor 54. However, the direct current voltage VDC is a constant value, i.e., the voltage level of the direct current voltage VDC can not be regulated. In addition, the only way of changing the rotational speed of the brushless DC motor 54 is through the pulse width modulation (PWM) signal provided by the motor controlling circuit 55, but if the rotational speed of the brushless DC motor 54 is regulated solely by the PWM signal, the noise caused by shifting in the electronic elements of the brushless DC motor 54 and the consumption of the motor controlling circuit 55 are both increased.